Application of centrifugal counter-current chromatography to the separation of macrolide antibiotic analogues. I. Selection of solvent systems based on solubility and partition coefficient investigations

As the first part of our studies on counter-current chromatography, the methodology for selecting suitable solvent systems was established based on detailed investigations of solubility and partition coefficients (log K) of macrolide antibiotic analogues. The solubility of two important macrolides, ascomycin and FK-506, was measured in a series of common solvents, where their polarities were ranked with dielectric constants. The partition coefficients of the two macrolides were compared in various binary, ternary, quaternary solvent systems. Hexane-tert.-butyl methyl ether-methanol-water system was selected based on suitable log K of solutes and hydrogen-bonding properties of solvents. In the further optimisation of composition proportions in the multicomponent solvent system, hexane-tert.-butyl methyl ether-methanol-water (1:3:6:5) showed the best solvent selectivity by giving the most prominent difference of partition coefficient (delta log K) between ascomycin and FK-506. With this solvent system, a baseline preparative separation of these two very closely related 23-membered macrolide antibiotics was successfully achieved by employing the newly introduced Quattro counter-current chromatograph.     

Austauschreaktionen an komplexgebundenen liganden von elementen der IV. Hauptgruppe : III. Darstellung von halogen-, pseudohalogen- und hydridokomplexen des typs π-C5H5Fe(CO)2SiX3

The complexes CpFe(CO)₂SiBr₃, CpFe(CO)₂SiI₃, CpFe(CO)₂SiBr₂(OMe), and CpFe(CO)₂SiI(NH-cyclo-C₆H₁₁)₂ are prepared by the reaction of CpFe(CO)₂SiR₃ (R = OMe, NH-cyclo-C₆H₁₁) with HBr, HI and CH₃I. Treating CpFe(CO)₂SiCl₃ with a large excess of NaN₃, KOCN or KSCN yields the first tri-pseudohalogensilyl—transition-metal-complexes. The compounds are characterized by IR and mass spectra. A new method of preparation of the already known complex CpFe(CO)₂SiH₃ is described starting from CpFe(CO)₂SiCl₃ and LiAlH₄.     

Solid Phase Extraction and Flame Atomic Absorption Spectrometric Determination of Trace Amounts of Zinc and Cobalt Ions in Water Samples

A simple and rapid method for the preconcentration of Co²⁺ and Zn²⁺ as their 2-guanidino-benzimidazole chelates is proposed using an octadecyl silica cartridge. The retained analytes were recovered with a mixture of 5mL of 0.01M HNO₃ and 5mL of methanol. The metal ions in the effluent were determined by flame atomic absorption spectrometry. The effect of different parameters, such as sample matrix, amount of ligand, type of eluent for elution of ions from cartridge, flow rates of sample solution and eluent, breakthrough volume, and limit of detection, were evaluated. The effects of various cationic and anionic interferences on the percent recovery of Co²⁺ and Zn²⁺ were also studied. Quantitative extraction efficiencies were obtained by elution of the cartridge with a minimal amount of solvent. Hence, with a typical preconcentration factor of 50, the limits of detections of the proposed method are 0.26 and 1.62ngmL^–1 for Zn²⁺ and Co²⁺, respectively. The method was applied to the determination of zinc and cobalt ions in different water samples.     

Osmotic Coefficients of Aqueous Solutions of Some Poly(oxyethylene) Glycols at the Freezing Point of Solution

Summary. The freezing temperatures of dilute aqueous solutions of some poly(oxyethylene) glycols (PEG, HO–(CH₂CH₂O) _n –H, n varying from 4 to 117) were measured over a solute to solvent mass ratio from 0.0100 to 0.3900. The second and third osmotic virial coefficient (A ₂₂ and A ₂₂₂) of poly(oxyethylene) glycols in aqueous solution were determined. The molecular weight dependence of the second virial coefficient can be described by a simple relation A ₂₂=2×10^–5 M _n ^1.86, and the third virial coefficient is A ₂₂₂=0.038A ₂₂ ². The activity coefficients of the solute were calculated using the Gibbs-Duhem equation as applied by Bjerrum. From the osmotic and activity coefficients the excess Gibbs energies of solution, as well as the respective partial molar functions of solute and solvent and the virial pair interaction coefficients for the excess Gibbs energies were estimated. The second and the third osmotic virial coefficients are correlated with the Mc-Millan-Mayer virial coefficients.     

Determination of the expiration date of chemical solutions

Thirty-five chemical solutions, acids, bases, complexing, argentometric, reducing, oxidising, salts and eluent mixtures, were studied continuously over a 7.5-month period. Twenty-seven remained reasonably stable and had acceptable expiration dates, which were equal to or more than 2 months longer than the established average deviation of ±2% relative to the initial value. Exceptions were made for potassium permanganate (0.1 M), perchloric acid (0.1 M) and disodium hydrogen phosphate (10%) solutions, as well as for HPLC eluent mixtures, which showed stability with expiration dates equal to stated values or shorter by 1 month. The eight chemical solutions presenting expiration dating higher than 6 months were hydrochloric acid (0.1 and 1 M), sulphuric acid (0.5 and 1.5 M), ethylenediamine tetraacetic acid (EDTA) (0.1 M), silver nitrate (0.1 M), ammonium thiocyanate (0.1 M) and iodine (0.1 M). The present data is a suitable guideline for the date of several chemical solutions routinely used in the analytical laboratories.     

Synthesis and Characterisation of Unsymmetrical Porphyrazines Containing Bis(hydroxyethylthio) Substituents

Summary. Unsymmetrical porphyrazines bearing a single peripheral bis(hydroxyethylthio) moiety were synthesised by mixed condensation of bis(2-hydroxyethylthio)maleonitrile and phthalonitrile. Complexation of the thioether groups of metal-free porphyrazine with PdCl₂ further lowered the intensity of the Q-band absorption of the porphyrazine core. The new compounds were characterised by elemental analyses, IR, ¹H NMR, UV-Vis, and mass spectra.     

The platinum catalyst [bpyrPtCl2] in superacidic solution

The methane oxidation catalyst [bpyrPtCl(2)] (bpyr = bis-pyrimidine) dissolves in superacidic HF/SbF(5) solution under formation of a dinuclear cation [H(2)bpyrPt(mu-Cl)(2)PtbpyrH(2)](6+). Two crystal forms are isolated, [Pt(2)Cl(2)bpyr(2)H(4)](6+)(SbF(6)(-))(4)(Sb(2)F(11)(-))(2).2HF (I) (triclinic, Ponemacr;, a = 814.8(2) pm, b = 1444.8(3) pm, c = 2300.5(5) pm, alpha = 89.627(4) degrees, beta = 84.285(4) degrees, gamma = 84.665(4) degrees, Z = 2) and [Pt(2)Cl(2)bpyrH(4)](6+)(Sb(2)F(11)(-))(6).4HF (II) (triclinic, Ponemacr;, a = 879.4(2) pm, b = 1170.4(3) pm, c = 1789.9(5) pm, alpha = 95.37(2) degrees, beta = 99.97(2) degrees, gamma = 100.41(2) degrees, Z = 1). The cation in I has an angle of 148.4(1) degrees between the two square plane platinum environments, while the cation in II is fully planar. The non-platinum-bound nitrogen atoms are all protonated in the superacidic medium.     

Extended traceability of pH: an evaluation of the role of Pitzer's equations

The 2002 IUPAC recommendation on pH (provisional) has taken its own philosophy to provide a basis for comparable and traceable assignment of a value, from a measurement, to the quantity pH. Whereas the substituted 1983 IUPAC recommendation relied heavily on precisely prescribed experimental techniques and procedures, the current recommendation defines a hierarchical relationship between references for comparison (primary and secondary standards) and objective criteria on the comparison of measurements with these standards. The recommendation aims at a traceability chain from the national metrological institution (NMI) level down to field and laboratory measurements. Currently, however, the traceability chain is developed to the level of certified reference materials (CRM), namely the above mentioned primary and secondary standards. To complete the traceability chain, several theoretical and practical aspects have to be pondered. In part, the methods for comparative assessment of different options have yet to be developed. As an illustrating example of the complexity of issues to be considered in a further extension of the traceability chain is estimation of the doubt associated with Pitzer coefficients. The Pitzer equations for activity coefficient modelling are explicitly mentioned in the 2002 IUPAC recommendation on pH (provisional) as enabling possible improvement in the ionic strength extrapolations to zero ionic strength. An assessment of uncertainty of ternary Pitzer coefficients is given for the first time.     

Facile synthesis of novel functionalized bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) derivatives

An improved and efficient synthetic route to four functionalized bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) derivatives 2-5 is reported. Tetrathiolate 1 was readily prepared from 2,2'-bis(1,3,4,6-tetrathiapentalen-5-one) under carefully controlled conditions. Subsequent reaction of 1 with selected primary alkyl halides affords new functionalized BEDT-TTF derivatives in good yields.     

All-solid-state planar miniature ion-selective chloride electrode

All-solid-state ion-selective electrodes with plastic membrane (poly(vinyl chloride) (PVC), bis(2-ethylhexyl) sebacate (DOS), methyltri-n-tetradecylammonium chloride (MTTACl)), a conducting poly(pyrrole) (PPy) film doped either with chloride ions (PPyCl) or hexacyanoferrate(II) ions (PPyFeCN), and glassy carbon (GC) or screen-printed graphite layer (S-PG) as an inner electric contact were investigated. All the electrodes show close to Nernstian response, but their lifetimes vary. The at least 2-months lifetime of screen-printed electrodes is only achieved for the electrodes containing PPyFeCN (cation-exchanging film). Shorter lifetime of other screen-printed electrodes, i.e. without PPy, or with PPyCl (anion-exchanging film), was attributed to the diffusion of anionic products of the hydrolysis of organic components of the graphite paste used to prepare the electric contact. The properties of miniature, screen-printed electrodes comprising PPyFeCN solid contact, were comparable to those ion-selective electrodes with PPy solid contact (regardless the ion-exchanging characteristic of the polymer) deposited on GC electric contact.